In the conventional method employed for the manufacture of molded records such as audio records or the more recently developed capacitive electronic discs, the signal information to be molded into the record or disc is initially cut into a recording substrate along a spiral groove. The recorded substrate is then prepared for electroforming. The surface of wax or laquer substrates used for audio records are activated so as to accept electrodeposited metal. Metal substrates such as the copper substrates used for capacitive electronic discs are passivated so as to prevent adhesion of the electrodeposited metal to the surface of the metal substrate.
The recorded surface of the substrate is then replicated by electroforming a metal such as nickel on the recorded surface of the substrate to produce a master on the surface of the recorded substrate. The recorded surface of the resulting metal master is then passivated and in turn is replicated to form a series of mothers. The recorded surface of the resulting mothers are in turn passivated and replicated to provide a series of stampers. The resulting metal stampers are the parts used to mold the audio records or capacitive electronic discs. The above sequential process of making masters, mother and stampers is referred to as matrixing.
One of the most important pieces of equipment used in the matrixing process is the cathode head. The cathode head is the apparatus on which the part to be replicated, referred to as a matrix, is mounted during electroforming of a replica on the surface thereof. The cathode head is secured to the cathode of an electroforming apparatus and is generally rotated in the electrolyte in the electroforming apparatus during matrixing.
Various types of cathode heads have heretofore been suggested in the art for use in the matrixing process. One widely used type of cathode head had a flat disc configuration and was used in combination with a u-shaped rubber band-like outer edge seal. Using the above type of cathode head the matrix was initially secured to the cathode head at its center. A preplate of metal was then applied over the entire surface of the matrix with care being taken to insure that a thin layer of metal extended over the outer edge of the matrix. The thin layer of deposited metal was used to physically prevent the preplated metal and metal subsequently deposited on the matrix from separating from the surface of the matrix during electroforming. After the required thickness of preplated metal was applied to the surface of the matrix the preplating was discontinued and the U-shaped rubber ring was placed about the outer edge of the matrix so as to form a seal over the outer edge to prevent further plating of the edge portion. The electroforming was then continued until a replica with the desired thickness was obtained. The apparatus and the procedure described above did not prove to be completely satisfactory in practice. The discontinuation of the plating process in order to install the rubber edge shield on the matrix results in a substantial reduction in the quality of the plating. A further significant problem encountered was that the plating of metal over the edges of the matrix results in considerable difficulty being encountered when separating the replica from the matrix with the resulting replicas having rough irregular outer edges.
Cathode heads have also been suggested which had rubber backs and integral edge seals to secure the matrix to the cathode head during electroforming. A cathode head of this type is disclosed by L. R. Porrata et al. in U.S. Pat. No. 3,414,502 issued Dec. 3, 1968 entitled "Electroplating Apparatus for Use With Phonograph Record Matrix." Apparatus such as disclosed by Porrata et al. was found to be unsatisfactory in practice in that it was difficult to physically insert a matrix into the cathode head. Furthermore, the rubber edge shield could not be tightly secured to the matrix and this allows leakage of electrolyte about the edges of the matrix to the back side of the matrix, causing undesirable edge and back plating.
Another type of cathode head which has heretofore been suggested in the prior art to improve the quality of the matrixing of masters, molds, and stampers is disclosed by Whitehurst in U.S. Pat. No. 4,259,166 entitled "Shield For Plating Substrates." The device disclosed by Whitehurst provides a masking apparatus which has certain distinct advantages over the cathode heads heretofore mentioned but still had the disadvantage that it was difficult to assemble and problems were still encountered in separating electroformed replicas from the matrixes.
A significantly improved type of cathode head was disclosed by Prusak et al. in U.S. Pat. No. 4,341,613 issued July 22, 1982 entitled "Apparatus for Electroforming." The Prusak et al. cathode has a flat disc shape support which is threaded on its outer edge. A matrix to be replicated is secured at the center thereof to the cathode with a cathode knob. A threaded outer ring is provided which includes a flat seal designed to engage the outer edge of the matrix to prevent electrolyte from leaking past the seal to the outer edge of the matrix. The threaded outer ring is screwed onto the threaded outer edge of the flat disc shape member and should be tightened until an electrolyte tight seal is obtained. In practice the Prusak et al. cathode head has proven to be highly successful in almost all respects. Problems have, however, been encountered in forming an electrolyte tight seal at the outer edge of the matrix.
What would be highly advantageous would be a cathode head having the advantageous features of the Prusak et al. apparatus but which would further include means for providing an improved electrolyte seal so as to prevent leakage of electrolyte to the outer edges of the matrix during electroforming.